The present invention relates to a filling machine for filling a plurality of containers with fluid such as beverages or drugs, and in particular, to, a filling machine for monitoring a flow of fluid injected into each container by using an electromagnetic flow meter in order to fill each container with a fixed amount of fluid.
As a method of controlling fluid filled in each container to be a fixed amount, there are a method of monitoring weight of a container in which the fluid is injected and a method of monitoring a flow through a filling pipe for injecting the fluid into the container. As for the method of monitoring a flow, a vortex flow meter, an oval flow meter, an electromagnetic flow meter and so on can be utilized as a flow meter. As the vortex flow meter and the oval flow meter have structures in a channel, there may be deposits generated in the channel. For this reason, it is not desirable to use the vortex flow meter and the oval flow meter from the viewpoint of sanitation and maintenance. Thus, a filling machine using an electromagnetic flow meter having no structures in the channel is commercialized.
FIG. 12 is a block diagram showing overall configuration of a conventional filling machine using the electromagnetic flow meter.
This filling machine has a plurality of filling pipes 202a to 202n placed thereon. The filling pipes 202a to 202n have valves 203a to 203n provided respectively. In addition, the filling pipes 202a to 202n have the electromagnetic flow meters comprised of detectors 205a to 205n and converters 206a to 206n provided respectively. The electromagnetic flow meters of the filling pipes 202a to 202n calculate a flow in filling pipes 202a to 202n based on electromotive force generated by applying an alternating field to fluid in the filling pipes 202a to 202n respectively. Flow signals indicating the flows calculated by the converters 206a to 206n are outputted to control sections 208a to 208n respectively.
The control sections 208a to 208n control opening and closing of the valves 203a to 203n provided for the filling pipes 202a to 202n respectively. The control sections 208a to 208n open the valves 203a to 203n respectively, and then calculate a total sum of the fluid injected into containers 201a to 201n based on the flow signals outputted from converters 206a to 206n of the electromagnetic flow meters, and close the valves 203a to 203n when the total sum reaches a set value. The above set value with reference to which the control sections 208a to 208n close the valves 203a to 203n is individually adjusted at the control sections 208a to 208n before operation of the filling machine so as to fill all the containers 201a to 201n with a fixed amount of the fluid even if temperature, humidity and so on change.
Next, the electromagnetic flow meter used for the conventional filling machine shown in FIG. 12 will be further described. While the electromagnetic flow meter comprised of the detector 205a and the converter 206a will be described as an example hereafter, the electromagnetic flow meters comprised of the detectors 205b to 205n and the converters 206b to 206n also have the same configuration respectively.
FIG. 13 is a block diagram showing an example of configuration of the electromagnetic flow meter comprised of the detector 205a and the converter 206a. 
An exciting current 263c of a predetermined frequency is outputted from an exciting section 263 to exciting coils 251a, 251b (a frequency of the exciting current 263c is referred to as an exciting frequency). The exciting coils 251a, 251b are excited by the exciting current 263c to generate an alternating field. If such a magnetic field is applied to the fluid in the filling pipe 202a, electromotive force having an amplitude proportionate to average flow velocity is generated by electromagnetic induction in a direction orthogonal to both the directions of the magnetic field and of the flow of the fluid. An AC voltage signal based on this electromotive force is taken out by electrodes 252a, 252b mounted opposite an inner wall of the filling pipe 202a. 
The AC voltage signal taken out by electrodes 252a, 252b is AC-amplified by an amplifier 265 and is outputted as an AC flow velocity signal 265s to a sample hold section 266. On the other hand, sampling signals 264s, 264t are outputted from a sampling control section 264 to the sample hold section 266. The sampling signals 264s, 264t are the signals indicating timings for sampling a positive side and a negative side of the AC flow velocity signal 265s respectively, and have the same frequency as the exciting frequency. In the sample hold section 266, the AC flow velocity signal 265s is sampled according to the sampling signals 264s, 264t, and a DC flow velocity signal 266s of which DC potential changes according to the average flow velocity is outputted.
The DC flow velocity signal 266s outputted from the sample hold section 266 is converted into a digital signal by an A/D converter 267 and then inputted to a processor 268. The processor 268 calculates an average flow in the filling pipe 202a by performing predetermined processing to the input signal. The digital signal indicating this average flow has the same frequency as the exciting frequency, and is outputted as a flow signal from an output section 269 to the control section 208a shown in FIG. 12.
FIG. 14 is a timing chart showing signals of the sections of the electromagnetic flow meter shown in FIG. 13, where (A) is a voltage (hereafter, referred to as an exciting voltage) 263v applied to the exciting coils 251a, 251b by the exciting section 263, (B) is the AC flow velocity signal 265s outputted from the amplifier 265, (C) and (D) are the sampling signals 264s, 264t outputted from the sampling control section 264 respectively, and (E) is the DC flow velocity signal 266s outputted from the sample hold section 266.
As the exciting voltage 263v is a rectangular wave as shown in FIG. 14(A), differential noise occurs when polarity of the exciting voltage 263v switches. This differential noise is superimposed on the AC voltage signal based on the electromotive force generated by magnetic field application. Therefore, a spike appears at the beginning of each pulse of the AC flow velocity signal 265s as shown by solid lines in FIG. 14(B).
In addition, in the case where commercial power is supplied to the electromagnetic flow meter shown in FIG. 13, the AC noise derived from this commercial power is superimposed on the AC flow velocity signal 265s via the filling pipe 202a. However, if the frequency of the exciting voltage 263v is 1/(an even number) of the frequency of the commercial power, an error based on the AC noise can be eliminated. Moreover, the dotted lines in FIG. 14(B) indicate waveforms in the cases where the frequency Of the exciting voltage 263v is xc2xd of the frequency of the commercial power, that is, 25 Hz or 30 Hz.
Thus, the electromagnetic flow meter shown in FIG. 13 has a timing signal generating section 262 for extracting timing from commercial power 209. This timing signal generating section 262 generates a timing signal 262a of 50 Hz or 60 Hz for instance based on the timing extracted from commercial power 209. This timing signal 262a controls timing of the exciting section 263 and the sampling control section 264. At this time, it is possible, by setting sampling periods by the sampling signals 264s, 264t at the end of each pulse of the AC flow velocity signal 265s as shown in FIG. 14(C) and (D), to eliminate both an error based on the differential noise and an error based on the AC noise.
In this case, however, the frequency at which the flow signals are outputted from the converter 206a is 25 Hz or 30 Hz at most as with the exciting frequency. FIG. 15 is a diagram showing a relationship between the flow in the filling pipe 202a from opening till closing of the valve 203a (alternate long and short dash line) and the flow signals outputted from the converter 206a (solid lines). The horizontal axis of this diagram is time, and the vertical axis is a flow. As seen from this diagram, in the case of estimating the amount injected into the container 201a from the flow signals, errors become significant if the frequency of the flow signals is small. There has been a problem that, in the case of reducing filling time by increasing a flow per unit time or in the case of filling a small container with fluid, the errors become so significant at the above frequency that all the containers 201a to 201n cannot be filled with a fixed amount of fluid with good reproducibility.
FIG. 16 is a block diagram showing another example of configuration of the electromagnetic flow meter comprised of the detector 205a and the converter 206a. This diagram shows the same sections as in FIG. 13 by using the same symbols.
In the electromagnetic flow meter shown in FIG. 16, a timing signal generating section 362 performs frequency division of a clock signal 361s outputted from a clock signal generating section 361 to generate a timing signal 362s. It is possible to render the frequency of the timing signal 362s higher than 50 Hz or 60 Hz by adjusting a ratio of frequency division. Thus, It is possible to render the output frequency (that is, an exciting frequency) of the flow signal higher than 25 Hz or 30 Hz.
However, in the case of using the electromagnetic flow meter shown in FIG. 16 for a filling machine, there has been the following problem. FIG. 17 is a timing chart for describing this problem, where (A) is the exciting voltage 263v of the converter 206b, (B) and (C) are the exciting voltage 263v of the converter 206a and the AC flow velocity signal 265s. The converters 206a and 206b are the converters of the electromagnetic flow meters provided for adjacent filling pipes 202a and 202b respectively.
The filling machine shown in FIG. 12 has the filling pipes 202a to 202n placed adjacently since it is necessary to consecutively fill a plurality of containers 201a to 201n. In particular, in the case where the containers 201a to 201n are small, degree of adhesion of the filling pipes 202a to 202n becomes considerably high. In such a case, the differential noise occurring on switching rectangular wave excitation mutually affect the electromagnetic flow meters as leakage flux from the exciting coils 251a, 251b.
On the other hand, in the case of the electromagnetic flow meter shown in FIG. 16, the converters 206a to 206n determine excitation timing based on the individual clock signal 361s so that minute variations arise in the exciting frequencies among the electromagnetic flow meters. In such a case, even if excitation of the converters 206a to 206n is in synchronization at the beginning, there arise variations gradually over the course of time. And if polarity of the exciting voltage 263v of the converter 206b switches during the sampling period (the diagonally shaded area in FIG. 17 (C)) of the converter 206a (FIG. 17 (A)), an error is included in the flow signal from the converter 206a. A spike occurs to the AC flow velocity signal 265s due to an effect of the differential noise from the adjacent electromagnetic flow meter, and the spike is sampled.
The error included in the flow signal at this time is an uncertain error, which cannot be eliminated even by adjustment before operation of the filling machine. For this reason, amounts of filling vary among a plurality of containers 201a, which are sequentially filled with fluid from the filling pipe 202a. To be more specific, there has been a problem that the reproducibility of the amounts of filling deteriorates if the electromagnetic flow meter shown in FIG. 16 is used.
The present invention has been devised in order to solve such conventional problems, and its object is to provide the filling machine capable of filling with fluid in a short time with good reproducibility. Another object is to provide the filling machine capable of filling a small container with fluid with good reproducibility.
To attain such objects, the filling machine of the present invention has a plurality of filling pipes placed in proximity to one another for injecting fluid into each of a plurality of containers, a valve provided for each of the filling pipes for opening and closing each of the filling pipes based on an open signal and a close signal respectively, an electromagnetic flow meter provided for each of the filling pipes for calculating a flow based on electromotive force generated by applying an alternating field to the fluid in each of the filling pipes and outputting a flow signal, a control means for outputting the open signal to each of the valves, and also outputting the close signal to each of the valves based on the flow signal outputted from each of the electromagnetic flow meters after outputting the open signal so as to fill each of the containers with a fixed amount of the fluid, exciting frequency setting means for setting an exciting frequency in each of the electromagnetic flow meters at a desired frequency, and synchronization means for synchronizing excitation timing in each of the electromagnetic flow meters. Such configuration allows the excitation timing to be synchronized among the electromagnetic flow meters even if the exciting frequency is set higher 25 Hz or 30 Hz for instance. Thus, it can prevent the effect of the differential noise from the adjacent electromagnetic flow meter from being given to the flow signal.
In this case, the exciting frequency setting means is comprised of a synchronous signal generating means included in one of the electromagnetic flow meters for generating a synchronous signal having a frequency of the desired value by performing frequency division of a clock signal of this electromagnetic flow meter, and the synchronization means is comprised of a synchronous signal line for transmitting the synchronous signal generated in one of the electromagnetic flow meters to all the other electromagnetic flow meters and exciting means included in each of the electromagnetic flow meters for performing excitation in synchronization with the synchronous signal. Such configuration allows excitation of all the electromagnetic flow meters to be in synchronization with the synchronous signal generated by one electromagnetic flow meter.
Or the exciting frequency setting means is comprised of a timing signal generating means included in each of the electromagnetic flow meters for generating a first timing signal having a frequency of the desired value by performing frequency division of the clock signal of the electromagnetic flow meter, and the synchronization means is comprised of a timing correcting means included in each of the electromagnetic flow meters for correcting timing of the first timing signal in a predetermined cycle based on an AC signal acquired in common by all of the electromagnetic flow meters and exciting means included in each of the electromagnetic flow meters for performing excitation in synchronization with the first timing signal. Even if variations arise to timing of the first timing signal generated by each of the electromagnetic flow meters, they can be corrected based on an AC signal acquired in common by the electromagnetic flow meters, and so it allows excitation of all the electromagnetic flow meters to be in synchronization.
In this case, the AC signal utilized by said synchronization means is an AC current supplied in common from an AC power supply to each of the electromagnetic flow meters. Or it Is AC noise generated by the AC current outputted from an AC power supply.
In addition, the timing correcting means of the synchronization means has means for extracting a second timing signal from the AC signal and means for correcting the timing of the first timing signal at a point in time when the timing of the first timing signal and the timing of the second timing signal approximately correspond with each other.